Researchers have been speculating that the flu vaccine might spark a broad immune response that could help prevent other infections, including Covid-19. And while there is growing interest in this theory, and other studies have found similar associations, it’s hard to know whether these effects are causal or just coincidental, Dr. Fradin said.
The best way to prevent Covid-19, she added, is to get a Covid-19 vaccine.
How can I tell if I have the flu, Covid, a cold or allergies?
It can be challenging to distinguish between these conditions because they have many overlapping symptoms. For instance, both the flu and Covid-19 can cause fever, chills, cough, shortness of breath, fatigue, sore throat, runny nose, body aches, headache, vomiting and diarrhea. Therefore, “the only way to distinguish reliably between the two illnesses is to get tested,” Dr. Gandhi said. (One exception is that Covid-19 can cause a loss of taste and smell, but the flu does not, she said.)
There are now combined tests available at some doctor’s offices that can distinguish between flu, SARS-CoV-2 and respiratory syncytial virus (R.S.V.), a common and typically mild respiratory virus that can cause more serious symptoms in infants and older adults. Most of these tests are not covered by health insurance, though, Dr. Fradin said. They can run around $250, although costs may vary, she said.
Some cold and allergy symptoms might overlap with those from the flu or Covid-19 (like cough, runny nose and congestion), but symptoms of colds and allergies are typically more mild, and are usually limited to the nose, throat and chest. In kids, however, Covid-19 can present a lot like a cold. So it may be wise for kids with cold symptoms to get a Covid-19 test, Dr. Fradin said.
What should I do if I get the flu?
If you think you have the flu, a good first step is to call or set up a telemedicine visit with your doctor, if you can. “A virtual visit may suffice and your doctor could advise on next steps for testing,” Dr. Gandhi said, to determine if you have the flu, Covid-19, both or something else.
If you do have the flu, you may be eligible to receive antiviral drugs that can reduce symptom severity, Dr. Gandhi said. Also, drink plenty of water and other clear liquids, take over-the-counter pain relievers if needed and avoid contact with others. If possible, stay home for at least 24 hours after your fever is gone.
What if I get the flu and Covid-19 at the same time?
Simultaneous infections like these have so far been rare. A spring 2020 study in New York City, for instance, found that after testing about 1,200 Covid-19 patients for co-infection with other respiratory viruses, like influenza, only 3 percent had simultaneous infections.
